JP2022082864A - Image forming apparatus - Google Patents

Abstract

To provide an image forming apparatus that can prevent transfer deviation with a simple configuration.SOLUTION: An image forming apparatus comprises: an intermediate transfer belt 54; primary transfer rollers 60 that face photoreceptor drums 36 with the intermediate transfer belt therebetween; a driving roller 56 that rotates the intermediate transfer belt; a secondary transfer roller 44 that faces the driving roller with the intermediate transfer belt therebetween; an auxiliary roller 64 that is provided between a photoreceptor drum at a most downstream position and the driving roller; and a connection roller 72 that is in contact, on its outer peripheral surface, with the driving roller and an outer peripheral surface of the auxiliary roller to transmit a rotation driving force of the driving roller to the auxiliary roller.SELECTED DRAWING: Figure 2

Description

The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus, for which a toner image is primaryly transferred from a plurality of photoconductor drums arranged side by side to an intermediate transfer belt, and a toner image is secondarily transferred from the intermediate transfer belt to paper. ..

An example of a conventional image forming apparatus is disclosed in Patent Document 1. In the image forming apparatus of Patent Document 1, a sheet-shaped member transporting device is applied to the intermediate transfer device, and the sheet-shaped member transporting device is a first roller (intermediate transfer belt) on which an endless belt (intermediate transfer belt) is stretched. A drive roller), a second roller (secondary transfer member) forming a pressure contact portion with the first roller sandwiching the endless belt, and a first drive portion for rotationally driving the endless belt. Further, this sheet-shaped member transporting device includes a fluctuation information acquisition means for acquiring fluctuation information of the endless belt, and a sheet-shaped member (printing medium) at a predetermined position of the endless belt on the upstream side of the pressure contact portion based on the acquired fluctuation. ) Is in contact with the variation detecting means for detecting the variation of the endless belt, the entry timing predicting means for predicting the entry timing of the pressure contact portion of the sheet-like member by the variation detection, and the first drive unit based on the timing. On the other hand, it is provided with a correction control means that performs feed-forward control and corrects the speed fluctuation of the endless belt that occurs when the sheet-shaped member enters the pressure contact portion.

Japanese Unexamined Patent Publication No. 2009-15287

The print medium for forming an image using the image forming apparatus includes not only plain paper such as A4 paper but also thick paper having a thickness larger than that of plain paper and having a strong stiffness. When forming an image on thick paper, an impact is applied to the intermediate transfer belt when the thick paper rushes into the secondary transfer nip portion, and the speed of the intermediate transfer belt is instantaneously increased. The effect of the momentary acceleration of the intermediate transfer belt is transmitted to the primary transfer nip portion, which may cause transfer deviation (distortion of the image).

In the technique of Patent Document 1, transfer deviation is avoided by performing feedforward control that cancels the speed fluctuation of the intermediate transfer belt. However, it is difficult to accurately perform feedforward control. Further, in the technique of Patent Document 1, a detector such as a rotary encoder for detecting the speed information of the intermediate transfer belt is required, and the control circuit is complicated, so that the manufacturing cost increases.

Therefore, the main object of the present invention is to provide a novel image forming apparatus.

Another object of the present invention is to provide an image forming apparatus capable of appropriately preventing transfer deviation with a simple configuration.

The first invention is an image forming apparatus that secondarily transfers a toner image primaryly transferred from each of a plurality of photoconductor drums to an intermediate transfer belt to a printing medium in a predetermined circumferential direction by a plurality of tension rollers. It is one of an intermediate transfer belt rotatably stretched, a plurality of primary transfer members provided so as to face each of a plurality of photoconductor drums with the intermediate transfer belt interposed therebetween, and a plurality of tension rollers. , A drive roller provided at a position downstream of the plurality of photoconductor drums in the circumferential direction to rotate the intermediate transfer belt, and a plurality of secondary transfer members provided so as to face the drive roller with the intermediate transfer belt interposed therebetween. One of the tension rollers, the auxiliary roller provided between the photoconductor drum and the drive roller arranged at the most downstream position in the circumferential direction, and the outer peripheral surface of the outer peripheral surface of the drive roller and the auxiliary roller. It is an image forming apparatus including a connecting roller that comes into contact with each of the outer peripheral surfaces and transmits the rotational driving force of the driving roller to the auxiliary roller.

According to the first invention, since the connecting roller rotates the auxiliary roller at the same peripheral speed as the drive roller, the auxiliary roller causes a momentary increase in the speed of the intermediate transfer belt when the thick paper rushes into the secondary transfer nip. It is dammed and prevents the impact from being transmitted to the primary transfer nip. Therefore, it is possible to appropriately prevent the occurrence of transfer deviation with a simple configuration without particularly requiring feedforward control or the like.

The second invention is subordinate to the first invention, and the intermediate transfer belt is stretched so as to be wound around an auxiliary roller at a predetermined winding angle.

According to the second invention, since the intermediate transfer belt is rotationally conveyed without slipping in a state where the intermediate transfer belt is wound around the auxiliary roller at a predetermined angle, even if the paper rushes into the secondary transfer nip, the intermediate transfer on the auxiliary roller is caused by the impact. The belt will not shift. That is, even if an impact is received, the impact is not transmitted to the photoconductor drum on the upstream side of the auxiliary roller, so that the occurrence of primary transfer deviation can be suppressed.

The third invention is dependent on the first or second invention, wherein the connecting roller has a shaft portion and a contact portion provided on the outer peripheral surface of the shaft portion and in contact with the drive roller and the auxiliary roller. The contact portions are provided only at both ends of the shaft portion.

The fourth invention is dependent on the third invention, and urges the arm member that rotatably supports the shaft portion of the connecting roller and the arm member in the direction of pressing the connecting roller against the drive roller and the auxiliary roller. It is equipped with a force member.

The fifth invention is dependent on any one of the first to fourth inventions, and includes a first disconnection mechanism for detaching the connecting roller from the drive roller and the auxiliary roller.

According to the fifth aspect of the invention, since the connecting roller can be separated from and detached from the drive roller and the auxiliary roller, even if the intermediate transfer belt is loosened between the drive roller and the auxiliary roller, the slack may occur. The slack can be eliminated.

The sixth invention is subordinate to the fifth invention, and the first disengagement mechanism includes a second arm member that rotatably supports the connecting roller around the axis of the drive roller by moving the arm member. ..

The seventh invention is subordinate to the fifth or sixth invention, and includes a second attachment / detachment mechanism for attaching / detaching a plurality of primary transfer members to a plurality of photoconductor drums, and the first attachment / detachment mechanism is a first attachment / detachment mechanism. 2 Connected to the disengagement mechanism, the disengagement of the plurality of primary transfer members with respect to the plurality of photoconductor drums and the disengagement of the coupling roller with respect to the drive roller and the auxiliary roller are interlocked.

According to the present invention, since the connecting roller rotates the auxiliary roller at the same peripheral speed as the drive roller, the auxiliary roller dampenes the momentary acceleration of the intermediate transfer belt when the thick paper rushes into the secondary transfer nip. , The impact is prevented from being transmitted to the primary transfer nip. Therefore, it is possible to appropriately prevent the occurrence of transfer deviation with a simple configuration without particularly requiring feedforward control or the like.

The above-mentioned object, other object, feature and advantage of the present invention will be further clarified from the detailed description of the following examples made with reference to the drawings.

It is a schematic sectional drawing which shows the internal structure of the image forming apparatus which is 1st Example of this invention. It is sectional drawing which shows the part around the secondary transfer nip part provided in the image forming apparatus of FIG. It is a perspective view which shows the part around the secondary transfer nip part of FIG. It is a schematic diagram which shows the disengagement mechanism of the primary transfer roller provided in the image forming apparatus of the 2nd Embodiment of this invention, and shows the state which the disengagement mechanism in the state which the primary transfer roller is in a contact position is seen from the back side. It is an illustration. It is a schematic diagram which shows the state which the primary transfer roller is in a separated position, and has seen from the back side. It is a schematic diagram which shows the disengagement mechanism of the connecting roller provided in the image forming apparatus of FIG. It is a schematic diagram which shows the state which the connecting roller is in the contact position, and the disengagement mechanism is seen from the front side. It is a schematic diagram which shows the state which the connecting roller is in the separated position, and has seen from the front side. It is a perspective view which shows the part around the secondary transfer nip part provided in the image forming apparatus of 3rd Embodiment of this invention.

[First Example]
With reference to FIG. 1, the image forming apparatus 10 according to an embodiment of the present invention is a multifunction device (MFP: Multifunction Peripheral) having a copying function, a printer function, a scanner function, a facsimile function, and the like, and is an electrophotographic system. Form a multicolor or monochromatic image on printing paper (printing medium). As will be described in detail later, the image forming apparatus 10 primary transfers the toner image from the plurality of photoconductor drums 36 arranged side by side to the intermediate transfer belt 54, and secondarily transfers the toner image from the intermediate transfer belt 54 to the printing paper. This is an intermediate transfer type image forming apparatus.

First, the configuration of the image forming apparatus 10 will be schematically described. In this specification, the front-back direction (depth direction) of the image forming apparatus 10 and its constituent members is defined with the surface facing the user's standing position, that is, the surface on the side where the operation unit (not shown) is provided, as the front surface (front surface). do. Further, the left-right direction (horizontal direction) of the image forming apparatus 10 and its constituent members is defined based on the state in which the image forming apparatus 10 is viewed by the user.

As shown in FIG. 1, the image forming apparatus 10 includes an apparatus main body 12 and an image reading apparatus 14 arranged above the apparatus main body 12.

The image reading device 14 includes a document mounting table 16 formed of a transparent material. A document holding cover 18 can be opened and closed on the upper side of the document mounting table 16 via a hinge or the like. The document holding cover 18 is provided with an automatic document feeder (ADF: Auto Document Feeder) 24 that automatically feeds the documents placed on the document placing tray 20 one by one to the image reading position 22. Be done. Further, on the front side of the document mounting table 16, an operation unit including a touch panel for receiving input operations such as a printing start instruction by a user and operation buttons is provided.

Further, the image reading device 14 has a built-in image reading unit 26 including a light source, a plurality of mirrors, an imaging lens, a line sensor, and the like. The image reading unit 26 exposes the surface of the document with a light source, and guides the reflected light reflected from the surface of the document to the imaging lens by a plurality of mirrors. Then, the reflected light is imaged on the light receiving element of the line sensor by the imaging lens. The line sensor detects the luminance and chromaticity of the reflected light imaged on the light receiving element, and generates image data based on the image on the surface of the document. As the line sensor, a CCD (Charge Coupled Device), a CIS (Contact Image Sensor) or the like is used.

The device main body 12 includes a control unit 28 including a CPU, a memory, and the like, an image forming unit 30, and the like. The control unit 28 transmits a control signal to each part of the image forming apparatus 10 in response to an input operation to an operation unit such as a touch panel, and causes the image forming apparatus 10 to perform various operations.

The image forming unit 30 includes an exposure unit 32, a developer 34, a photoconductor drum 36, a cleaner unit 38, a charger 40, an intermediate transfer unit 42, a secondary transfer roller 44, a fixing unit 46, and the like, and includes a paper feed cassette 48 or An image is formed on the printing paper conveyed from the manual paper feed tray 50, and the image-formed printing paper is discharged to the paper ejection tray 52. As the image data for forming an image on the printing paper, the image data read by the image reading unit 26, the image data transmitted from an external computer, or the like is used.

The image data handled by the image forming apparatus 10 corresponds to four color images of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, each of the developer 34, the photoconductor drum 36, the cleaner unit 38, and the charger 40 is provided so as to form four types of latent images corresponding to each color, whereby four image stations are provided. It is composed. The four image stations are arranged side by side.

The photoconductor drum 36 is an image carrier having a photosensitive layer formed on the surface of a conductive cylindrical substrate. The charger 40 is a member that charges the surface of the photoconductor drum 36 to a predetermined potential. Further, the exposure unit 32 is configured as a laser scanning unit (LSU) provided with a laser emitting unit, a reflection mirror, and the like, and by exposing the surface of the charged photoconductor drum 36, the electrostatic latency corresponding to the image data is obtained. An image is formed on the surface of the photoconductor drum 36. The developer 34 visualizes an electrostatic latent image formed on the surface of the photoconductor drum 36 with four-color (YMCK) toner. Further, the cleaner unit 38 removes the toner remaining on the surface of the photoconductor drum 36 after development and image transfer.

The intermediate transfer unit 42 includes an intermediate transfer belt 54, a drive roller 56, a driven roller 58, four primary transfer rollers (intermediate transfer rollers) 60, and the like, and is arranged above the photoconductor drum 36.

The intermediate transfer belt 54 is an endless band-shaped belt stretched so as to be rotatable (rotated) in a predetermined circumferential direction (counterclockwise in FIG. 1) by a plurality of tension rollers, and a plurality of belts arranged side by side. The outer peripheral surface (lower surface) of the photoconductor drum 36 is arranged along the outer peripheral surface (lower surface). The plurality of tension rollers include a drive roller 56, a driven roller 58, a backup roller 62, an auxiliary roller 64, and the like, and each of these tension rollers is provided so that the shaft portion extends in the front-rear direction. At the time of image formation, the outer peripheral surface of the intermediate transfer belt 54 is brought into contact with the surface of the photoconductor drum 36.

The drive roller 56 is provided on the downstream side of the intermediate transfer belt 54 in the circumferential direction with respect to the four primary transfer rollers 60, and stretches the right end portion of the intermediate transfer belt 54. The drive roller 56 is provided so as to be rotatable around its axis by a drive unit (not shown). Further, the outer peripheral portion (contact portion with the intermediate transfer belt 54) of the drive roller 56 is formed of a material having a large frictional force such as rubber in order to secure a frictional force (grip force) with respect to the intermediate transfer belt 54. .. Along with the rotational drive of the drive roller 56, the intermediate transfer belt 54 is orbitally moved in a predetermined circumferential direction.

The driven roller 58 is provided on the upstream side of the intermediate transfer belt 54 in the circumferential direction with respect to the four primary transfer rollers 60, and stretches the left end portion of the intermediate transfer belt 54. The driven roller 58 rotates with the orbital movement of the intermediate transfer belt 54 and applies a constant tension to the intermediate transfer belt 54 to prevent the intermediate transfer belt 54 from loosening.

The primary transfer roller 60 is a primary transfer member for transferring (primary transfer) the toner image formed on the corresponding photoconductor drum 36 to the intermediate transfer belt 54, and the photoconductors of each color sandwich the intermediate transfer belt 54. It is arranged at each position facing the drum 36. That is, a primary transfer nip portion is formed between the photoconductor drum 36 and the primary transfer roller 60. By using these four primary transfer rollers 60 to sequentially superimpose and transfer the toner images of each color formed on each photoconductor drum 36 on the intermediate transfer belt 54, a multicolor toner image is formed on the intermediate transfer belt 54. It is formed.

Further, each primary transfer roller 60 can be displaced in the direction of detachment with respect to the corresponding photoconductor drum 36 by the detachment mechanism 70 (see FIG. 2). That is, each of the primary transfer rollers 60 releases the contact position where the intermediate transfer belt 54 is pressed from the inner peripheral surface side to bring the intermediate transfer belt 54 and the photoconductor drum 36 into contact with each other, and the pressure on the intermediate transfer belt 54 is released. The photoconductor drum 36, the intermediate transfer belt 54, and the primary transfer roller 60 can be displaced to separate positions. Further, the disengagement mechanism 70 can have, for example, all the primary transfer rollers 60 at the contact position during color printing and only the black primary transfer roller 60 at the contact position during monochrome printing.

The backup roller 62 is provided between the primary transfer roller 60 (in this embodiment, the primary transfer roller 60 for black) and the drive roller 56 arranged on the most downstream side in the circumferential direction of the intermediate transfer belt 54. The backup roller 62 is a tension roller for keeping the lower portion of the intermediate transfer belt 54 horizontal, that is, allowing the intermediate transfer belt 54 to continue in a straight line even after passing through the primary transfer roller 60 for black. Therefore, the intermediate transfer belt 54 rotates in a driven manner as it orbits. Further, a resist sensor (not shown) is provided below the backup roller 62, and the backup roller 62 also has a function of keeping the distance between the resist sensor and the outer peripheral surface of the intermediate transfer belt 54 constant.

The auxiliary roller 64 is located between the black primary transfer roller 60 and the drive roller 56, in this first embodiment, on the downstream side of the backup roller 62 in the circumferential direction of the intermediate transfer belt 54 and on the upstream side of the drive roller 56. It is provided at the position. The auxiliary roller 64 is a tension roller for setting the secondary transfer nip portion to an appropriate length. The intermediate transfer belt 54 is stretched on the auxiliary roller 64 so as to be wound at an angle of the winding angle α in the image forming state (see FIG. 2).

Further, the secondary transfer roller 44 is a secondary transfer member for transferring the toner image formed on the intermediate transfer belt 54 to the printing medium so as to face the drive roller 56 with the intermediate transfer belt 54 interposed therebetween. It will be provided. When the printing paper passes through the secondary transfer nip portion between the secondary transfer roller 44 and the intermediate transfer belt 54, the toner image formed on the intermediate transfer belt 54 is transferred to the printing paper.

The fixing unit 46 includes a heat roller and a pressure roller, and is arranged above the secondary transfer roller 44. The heat roller is set to have a predetermined fixing temperature. When the printing paper passes through the nip area (fixing nip portion) between the heat roller and the pressure roller, the toner image transferred to the printing paper is heated and pressure-welded, and the toner image is heated with respect to the printing paper. Be fixed.

In such an apparatus main body 12, printing paper from the paper feed cassette 48 or the manual paper feed tray 50 is discharged via the resist roller 68, the secondary transfer roller 44 (secondary transfer nip portion), and the fixing unit 46. A first paper transport path L1 for feeding to the paper tray 52 is formed. Further, when double-sided printing is performed on the printing paper, the printing paper after the printing on the front side is completed and the printing paper has passed through the fixing unit 46 is transferred to the first paper on the upstream side in the paper transport direction of the secondary transfer roller 44. A second paper transport path L2 for returning to the transport path L1 is formed. The first paper transport path L1 and the second paper transport path L2 are appropriately provided with a plurality of transport rollers 66 for providing an auxiliary propulsive force to the printing paper.

The resist roller 68 is also called a paper stop roller (PS roller). For example, the resist roller 68 stands by (temporarily stops) in a state of sandwiching the printing paper conveyed by the conveying roller 66, and starts conveying the printing paper in synchronization with the intermediate transfer unit 42. At this time, the resist roller 68 is rotated at a peripheral speed slightly higher than the peripheral speed of the intermediate transfer belt 54 (that is, the drive roller 56). This is because the printing paper is conveyed between the resist roller 68 and the secondary transfer nip portion in a slightly bent state, and the transfer misalignment due to the printing paper being pulled between them is prevented. be.

When performing single-sided printing in the image forming apparatus 10, the printing paper is guided from the paper cassette 48 or the manual paper feed tray 50 to the first paper transport path L1 one by one, and is conveyed to the resist roller 68 by the transport roller 66. Will be done. Then, the resist roller 68 conveys the printing paper to the secondary transfer roller 44 at the timing when the tip of the printing paper and the tip of the image information on the intermediate transfer belt 54 match, and the toner image is transferred onto the printing paper. .. After that, the unfixed toner on the printing paper is heat-fixed by passing through the fixing unit 46, and the paper is discharged onto the paper ejection tray 52.

On the other hand, when double-sided printing is performed, when the printing on the front side is completed and the rear end portion of the printing paper that has passed through the fixing unit 46 reaches the transport roller 66 near the output tray 52, the transport roller 66 is used. By rotating in the reverse direction, the printing paper runs in the reverse direction and is guided to the second paper transport path L2. The printing paper guided to the second paper transport path L2 is conveyed by the transport roller 66 through the second paper transport path L2, and is guided to the first paper transport path L1 on the upstream side of the resist roller 68 in the paper transport direction. At this point, the front and back sides of the printing paper are reversed, and then the printing paper passes through the secondary transfer roller 44 and the fixing unit 46 via the resist roller 68, so that printing is performed on the back side of the printing paper.

The printing paper used in such an image forming apparatus 10 includes not only plain paper such as A4 paper, but also thick paper (postcards, envelopes, business cards, OHP films, etc.) that is thicker and stronger than plain paper. .. Here, when forming an image (printing) on plain paper, there is no particular problem, but when forming an image on thick paper, the toner image transferred from the photoconductor drum 36 to the intermediate transfer belt 54 at the primary transfer nip portion. Transfer misalignment may occur.

The cause of the transfer deviation will be briefly described. There is some slack in the lower portion of the intermediate transfer belt 54, that is, the portion of the intermediate transfer belt 54 that passes through each primary transfer nip. Further, the resist roller 68 is rotated at a peripheral speed slightly higher than the peripheral speed of the intermediate transfer belt 54. Therefore, the impact applied to the intermediate transfer belt 54 when the thick paper rushes into the secondary transfer nip portion causes the intermediate transfer belt 54 to momentarily accelerate, and the slack in the lower portion of the intermediate transfer belt 54 is secondary transfer. It will be instantaneously drawn to the nip part side. That is, the impact of the thick paper (effect of increasing the speed of the intermediate transfer belt 54) spreads to the primary transfer nip portion, and the positions of the primary transfer nip portion and its peripheral portion (image writing portion, etc.) are displaced, causing transfer deviation. Will end up.

Therefore, in this first embodiment, a connecting roller 72 for connecting the drive roller 56 and the auxiliary roller 64 is provided, and the rotational driving force of the drive roller 56 is transmitted from the connecting roller 72 to the auxiliary roller 64. Then, the drive roller 56 and the auxiliary roller 64 are rotated at the same peripheral speed, and the impact applied to the intermediate transfer belt 54 from the thick paper is blocked by the auxiliary roller 64 to prevent the occurrence of transfer deviation. Hereinafter, a specific description will be given.

As shown in FIGS. 2 and 3, the connecting roller 72 transmits the rotational driving force of the drive roller 56 to the auxiliary roller 64 to rotate the auxiliary roller 64 at the same peripheral speed as the peripheral speed of the drive roller 56. The member is provided so that its outer peripheral surface is in contact with each of the outer peripheral surface of the drive roller 56 and the outer peripheral surface of the auxiliary roller 64. That is, power is transmitted from the drive roller 56 to the auxiliary roller 64 by using the frictional force of the connecting roller 72.

Here, it is also conceivable to use a gear mechanism as a member for transmitting the rotational driving force of the driving roller 56 to the auxiliary roller 64. However, when the gear mechanism is used, the peripheral speed of the drive roller 56 and the peripheral speed of the auxiliary roller 64 may be slightly deviated from each other. On the other hand, by transmitting power from the drive roller 56 to the auxiliary roller 64 by the frictional force of the connecting roller 72, the drive roller 56 and the auxiliary roller 64 can be rotated at the same peripheral speed.

Specifically, the connecting roller 72 has a shaft portion 72a whose both ends are rotatably supported by a bearing portion (not shown), and a contact portion 72b provided on the outer peripheral surface of the shaft portion 72a. The shaft portion 72a of the connecting roller 72 is provided so as to extend in parallel with the shaft portion of the drive roller 56 and the auxiliary roller 64, that is, in the front-rear direction.

The contact portion 72b of the connecting roller 72 is a portion that comes into contact with the drive roller 56 and the auxiliary roller 64. In this embodiment, the contact portion 72b is provided only at both ends (front end portion and rear end portion) of the shaft portion 72a, and is not provided at the central portion of the shaft portion 72a. As a result, the material cost can be reduced. The material of the contact portion 72b is not particularly limited as long as it can exert an appropriate frictional force against the drive roller 56 and the auxiliary roller 64, and the contact portion 72b is formed by using synthetic resin, rubber, or the like. Will be done. However, in order to prevent the high voltage to the primary transfer roller 60 from leaking through the connecting roller 72, it is preferable to form the contact portion 72b with a material having electrical insulation. The contact portion 72b may be a porous elastic body such as urethane having a large insulation resistance.

The material of the outer peripheral portion of the auxiliary roller 64 (the contact portion with the intermediate transfer belt 54 and the connecting roller 72) is not particularly limited as long as it can exert an appropriate frictional force against the intermediate transfer belt 54, but is thick paper. In order to properly dampen the momentary acceleration of the intermediate transfer belt 54 at the time of plunge, a material having a large frictional force, for example, silicone rubber and rubber such as EPDM (ethylene propylene diene rubber), is used to the outer peripheral portion of the auxiliary roller 64. It is preferable to form.

In the image forming apparatus 10 provided with such a connecting roller 72, when the thick paper rushes into the secondary transfer nip portion, the intermediate transfer belt 54 momentarily accelerates. This occurs because the resist roller 68 is rotated at a peripheral speed slightly higher than the peripheral speed of the intermediate transfer belt 54, as described above. However, since the rotational driving force of the drive roller 56 is transmitted to the auxiliary roller 64 by the connecting roller 72 and the auxiliary roller 64 rotates at the same peripheral speed as the drive roller 56, the instantaneous speed increase of the intermediate transfer belt 54 is not possible. , It is dammed by the auxiliary roller 64. That is, the auxiliary roller 64, which rotates at the same peripheral speed as the drive roller 56, acts as a brake (braking portion) for the intermediate transfer belt 54 that momentarily accelerates, and the accelerated portion of the intermediate transfer belt 54 is canceled out. The influence of the speed increase of the transfer belt 54 is prevented from spreading to the primary transfer nip portion. Therefore, the occurrence of transfer deviation due to the displacement of the primary transfer nip portion and its peripheral portion is appropriately prevented.

Further, the intermediate transfer belt 54 is stretched and conveyed while being wound around an auxiliary roller 64 that rotates at the same peripheral speed as the drive roller 56 at a winding angle α. Therefore, even if the thick paper rushes into the nip portion of the secondary transfer portion and collides with the intermediate transfer belt 54, the intermediate transfer belt 54 on the auxiliary roller 64 has a frictional force with the auxiliary roller 64 (within the range of the winding angle α). It does not move momentarily and shift by overcoming (occurring). That is, the impact generated in the secondary transfer nip portion is not transmitted to the photoconductor drum 36 arranged on the upstream side in the circumferential direction of the intermediate transfer belt 54 from the auxiliary roller 64, so that the transfer deviation occurs in the primary transfer nip portion. Can be stably suppressed.

As described above, according to the first embodiment, since the connecting roller 72 rotates the auxiliary roller 64 at the same peripheral speed as the drive roller 56, the intermediate transfer belt 54 when the thick paper rushes into the secondary transfer nip portion. The momentary speed increase is dammed by the auxiliary roller 64, and the impact is prevented from being transmitted to the primary transfer nip portion. Therefore, it is possible to appropriately prevent the occurrence of transfer deviation with a simple configuration without particularly requiring feedforward control or the like.
[Second Example]
Next, the image forming apparatus 10 according to the second embodiment of the present invention will be described with reference to FIGS. 4 to 8. This second embodiment is different from the above-mentioned first embodiment in that the connecting roller 72 is provided so as to be detachable from the drive roller 56 and the auxiliary roller 64. Since the configurations of the other parts are the same, the same reference numbers are given to the parts common to the above-mentioned first embodiment, and duplicate explanations are omitted or simplified.

In the second embodiment, the connecting roller 72 is provided with a disengagement mechanism (first disengagement mechanism) 74 that separates the connection roller 72 from the drive roller 56 and the auxiliary roller 64. Further, in the second embodiment, the detaching mechanism 74 of the connecting roller 72 is connected to the detaching mechanism (second detaching mechanism) 70 that detaches and contacts each primary transfer roller 60 to each photoconductor drum 36. The detachment of each primary transfer roller 60 with respect to each photoconductor drum 36 and the attachment / detachment of the connecting roller 72 with respect to the driving roller 56 and the auxiliary roller 64 are interlocked.

First, an example of the disconnection mechanism 70 of the primary transfer roller 60 will be briefly described with reference to FIGS. 4 and 5. In FIGS. 4 and 5, the connecting roller 72 and the disconnection mechanism 74 are omitted for the sake of simplicity. Further, as the disconnection mechanism 70, only the portion where the primary transfer roller 60 for black arranged on the most downstream side is detached is shown. Further, since FIGS. 4 and 5 are views of the detaching mechanism 70 as viewed from the back surface side, the left and right sides are reversed from those of FIGS. 7 and 8 and the like.

As shown in FIGS. 4 and 5, the disengagement mechanism 70 is a mechanism for disengaging the photoconductor drum 36 and the primary transfer roller 60 with the intermediate transfer belt 54 interposed therebetween. As described above, by the disengagement mechanism 70, each of the primary transfer rollers 60 presses the intermediate transfer belt 54 from the inner peripheral surface side to bring the intermediate transfer belt 54 and the photoconductor drum 36 into contact with each other. Then, the pressure on the intermediate transfer belt 54 is released so that the photoconductor drum 36, the intermediate transfer belt 54, and the primary transfer roller 60 can be displaced to separate positions.

The disengagement mechanism 70 includes a first arm member 80, a slide member 82, and the like. The first arm member 80 is formed in a substantially L shape, and the primary transfer roller 60 is rotatably supported at one end thereof. Further, the bent portion of the first arm member 80 is rotatably supported by a bearing portion (not shown), and the other end portion of the first arm member 80 moves in the left-right direction, whereby the first arm member 80 On the other hand, the primary transfer roller 60 supported by the end portion moves in the vertical direction. Further, the other end of the first arm member 80 has a bifurcated shape and is provided so as to sandwich the slide member 82.

The slide member 82 is provided so as to be reciprocally movable in the left-right direction. A cam contact member 84 is provided at one end of the slide member 82. A cam member 86 is fitted to the cam contact member 84. Further, a pressing portion 82a for pressing the other end of the first arm member 80 is formed on the back surface side of the slide member 82. Further, as can be clearly seen from FIG. 7, one end of the slide member 82 on the surface side and the other end of the first arm member 80 are connected by a first coil spring 88. The other end of the first arm member 80 is in the left direction (right direction in FIGS. 4 and 5), which is the direction away from the drive roller 56 by the first coil spring 88, that is, the direction in which the primary transfer roller 60 moves downward. Be urged to.

Then, the rotation of the cam member 86 is controlled by a cam motor (not shown), so that the slide member 82 is moved in the left-right direction, and accordingly, the primary transfer roller 60 is separated from the photoconductor drum 36 (vertical direction). Is displaced to. That is, as shown in FIG. 4, at the time of image formation, the slide member 82 is moved to the left side (right side in FIG. 4) by the cam member 86. At this time, the other end of the first arm member 80 is pulled to the left by the first coil spring 88, so that the first arm member 80 rotates, and the primary transfer roller 60 is moved downward and arranged at the contact position. Will be done. On the other hand, as shown in FIG. 5, during non-image formation such as during standby, the slide member 82 is moved to a position to the right (to the left in FIG. 4) by the cam member 86. At this time, the other end of the first arm member 80 is pushed to the right by the pressing portion 82a, so that the first arm member 80 rotates, and the primary transfer roller 60 is moved upward and arranged at a separated position. ..

Further, the disengagement mechanism 70 includes a second arm member 90 and a link member 92, and has a function of moving the backup roller 62 up and down in conjunction with the disengagement movement of the primary transfer roller 60. The second arm member 90 rotatably supports the backup roller 62 at one end thereof, and the other end portion is rotatably supported by the shaft portion of the auxiliary roller 64. Further, the other end of the second arm member 90 is connected to the other end of the slide member 82 via the link member 92.

Then, when the slide member 82 is moved to a position to the left during image formation, the second arm member 90 is rotated downward by the link member 92, and the backup roller 62 is moved to a lower position (substantially horizontal with the primary transfer roller 60). It is moved to the position where it is lined up with. On the other hand, when the slide member 82 is moved to a position closer to the right during non-image formation, the second arm member 90 is rotated upward by the link member 92, and the backup roller 62 is moved to an upper position.

Subsequently, an example of the detaching mechanism 74 of the connecting roller 72 will be described with reference to FIGS. 6 to 8. As described above, the disengagement mechanism 74 is a mechanism for separating the connecting roller 72 from the drive roller 56 and the auxiliary roller 64, and is connected to the disengagement mechanism 70 of the primary transfer roller 60.

As shown in FIG. 6, the disengagement mechanism 74 includes a third arm member 94 and a second coil spring 96. One end of the third arm member 94 rotatably supports the shaft portion 72a of the connecting roller 72, and the other end portion is rotatably supported by the shaft portion of the drive roller 56. That is, the connecting roller 72 can rotate about the shaft portion of the drive roller 56 as a fulcrum. Further, the end surface on the one end side of the third arm member 94 is formed in an arc shape.

On the other hand, the second arm member 90 included in the disengagement mechanism 70 is formed with a protrusion 98 extending in the front-rear direction. The tip of the protrusion 98 is connected to the tip of the third arm member 94 by a second coil spring 96. The tip of the third arm member 94 is urged downward (specifically, in the diagonally lower right direction) by the second coil spring 96, that is, in a direction in which the connecting roller 72 is pressed against the drive roller 56 and the auxiliary roller 64. Further, the protruding portion 98 of the second arm member 90 is also used as a pressing portion for pressing the end surface on the one end side of the third arm member 94.

Then, when the second arm member 90 is rotated downward at the time of image formation, one end of the third arm member 94 is pulled downward by the second coil spring 96, so that one end of the third arm member 94 is formed. Rotates downward. As a result, the connecting roller 72 is moved downward and is arranged at a contact position where the outer peripheral surface of the contact portion 72b abuts on the outer peripheral surface of the drive roller 56 and the outer peripheral surface of the auxiliary roller 64. On the other hand, when the second arm member 90 is rotated upward during non-image formation, the protrusion 98 pushes up one end of the third arm member 94, so that one end of the third arm member 94 is lifted. Rotate upward. As a result, the connecting roller 72 is moved upward and is arranged at a separated position where the outer peripheral surface of the contact portion 72b is separated from the outer peripheral surface of the drive roller 56 and the outer peripheral surface of the auxiliary roller 64.

That is, when the primary transfer rollers 60 are in the contact position during image formation (for example, all the primary transfer rollers 60 are in the contact position during color printing, and only the black primary transfer roller 60 is in the contact position during monochrome printing. The connecting roller 72 also comes into contact with the drive roller 56 and the auxiliary roller 64. Further, when all the primary transfer rollers 60 are separated from each other at the time of non-image formation, the connecting roller 72 is also separated from the drive roller 56 and the auxiliary roller 64.

By providing such a disengagement mechanism 74, even if the intermediate transfer belt 54 is loosened between the drive roller 56 and the auxiliary roller 64 when the connecting roller 72 is in the contact position. By moving the connecting roller 72 to a separated position and causing the auxiliary roller 64 to rotate in a driven manner with respect to the intermediate transfer belt 54, the slack in the intermediate transfer belt 54 can be easily eliminated. Further, by moving the connecting roller 72 in a disengaged manner in conjunction with the disengagement movement of the primary transfer roller 60, the disengagement movement (displacement) of the connecting roller 72 is appropriately executed without requiring special control. be able to.

As described above, according to the second embodiment, as in the first embodiment, the connecting roller 72 rotates the auxiliary roller 64 at the same peripheral speed as the drive roller 56, so that transfer deviation occurs with a simple configuration. Can be appropriately prevented.

Further, according to the second embodiment, since the connecting roller 72 can be detached from the drive roller 56 and the auxiliary roller 64, the intermediate transfer belt 54 is connected between the drive roller 56 and the auxiliary roller 64 by any chance. Even if slack occurs, the slack can be easily eliminated.

However, the above-mentioned disengagement mechanism 70,74 is merely an example, and the specific configuration of the disengagement mechanism 70,74 can be appropriately changed.

Further, the disengagement mechanism 74 of the connecting roller 72 does not necessarily have to be connected (interlocked) with the disengaging mechanism 70 of the primary transfer roller 60, and the disengaging mechanism 74 of the connecting roller 72 can be individually controlled. good. When the disconnection mechanism 74 of the connecting roller 72 can be individually controlled, for example, the drive roller 56 and the auxiliary roller 64 can be connected by the connecting roller 72 only when printing on thick paper. Whether the paper is plain paper or thick paper (that is, the type of paper) can be determined, for example, by providing a thickness detection unit in the image forming apparatus 10, and providing the image forming apparatus 10 with a thickness detecting unit. It is also possible to provide a button for selecting the type of paper in the operation unit to be operated, and execute the operation based on the selection operation.
[Third Example]
Subsequently, with reference to FIG. 9, the image forming apparatus 10 according to the third embodiment of the present invention will be described. In this third embodiment, the configuration of the connecting roller 72 is different from that of the first embodiment described above. Since the configurations of the other parts are the same, the same reference numbers are given to the parts common to the above-mentioned first embodiment, and duplicate explanations are omitted or simplified. Although not shown, the third embodiment may be provided with the same disengagement mechanism 74 as in the second embodiment.

Briefly, in this third embodiment, the contact portion 72b of the connecting roller 72 is provided over substantially the entire length of the shaft portion 72a. That is, the axial length of the contact portion 72b of the connecting roller 72 is set to be substantially the same as the axial length of the contact portion of the drive roller 56. As a result, the frictional force (grip force) of the connecting roller 72 with respect to the driving roller 56 and the auxiliary roller 64 is improved.

According to the third embodiment, as in the first embodiment, the connecting roller 72 rotates the auxiliary roller 64 at the same peripheral speed as the drive roller 56, so that the occurrence of transfer deviation is appropriately prevented with a simple configuration. be able to.

In each of the above-described embodiments, the image forming apparatus 10 is exemplified by a multifunction device in which a copying machine, a facsimile, a printer, or the like is combined. However, the image forming apparatus 10 may be any one of a copying machine, a facsimile, a printer, and the like, or It may be a multifunction device that combines at least two of these.

Further, in each of the above-described embodiments, a roller method using a secondary transfer roller 44 is adopted when the toner image formed on the outer peripheral surface of the intermediate transfer belt 54 is secondarily transferred to the printing paper, but the present invention is limited to this. Instead, a belt method using a secondary transfer belt can also be adopted. That is, the secondary transfer member may be a secondary transfer belt. Further, the primary transfer member may be a pad member.

Further, the auxiliary roller 64 may be provided at least between the primary transfer roller 60 arranged on the most downstream side and the drive roller 56, and must have a function of setting the length of the secondary transfer nip portion. There is no. For example, the backup roller 62 for keeping the intermediate transfer belt 54 in a straight line can be also used as the auxiliary roller 64, or the auxiliary roller 64 dedicated to the braking use of the intermediate transfer belt 54 can be provided.

In addition, the specific component shapes and dimensions mentioned above are merely examples, and can be appropriately changed as needed, such as product specifications.

10 ... Image forming device 12 ... Device main body 14 ... Image reading device 36 ... Photoreceptor drum 42 ... Intermediate transfer unit 44 ... Secondary transfer roller (secondary transfer member)
54 ... Intermediate transfer belt 56 ... Drive roller 60 ... Primary transfer roller (primary transfer member)
64 ... Auxiliary roller 70 ... Separation mechanism (second separation mechanism)
72 ... Connecting roller 72a ... Shaft part 72b ... Contact part 74 ... Detachment mechanism (first disengagement mechanism)

Claims (7)

An image forming apparatus that secondarily transfers a toner image primaryly transferred from each of a plurality of photoconductor drums to an intermediate transfer belt to a printing medium.
The intermediate transfer belt, which is rotatably stretched in a predetermined circumferential direction by a plurality of tension rollers,
A plurality of primary transfer members provided so as to face each of the plurality of photoconductor drums with the intermediate transfer belt interposed therebetween.
A drive roller, which is one of the plurality of tension rollers and is provided at a position downstream of the plurality of photoconductor drums in the circumferential direction to rotate the intermediate transfer belt.
A secondary transfer member provided so as to face the drive roller with the intermediate transfer belt interposed therebetween.
One of the plurality of tension rollers, an auxiliary roller provided between the photoconductor drum and the drive roller arranged at the most downstream position in the circumferential direction, and an outer peripheral surface of the drive roller. An image forming apparatus comprising a connecting roller that comes into contact with each of the outer peripheral surface and the outer peripheral surface of the auxiliary roller and transmits the rotational driving force of the driving roller to the auxiliary roller. The image forming apparatus according to claim 1, wherein the intermediate transfer belt is stretched so as to be wound around the auxiliary roller at a predetermined winding angle. The connecting roller has a shaft portion and a contact portion provided on the outer peripheral surface of the shaft portion and in contact with the drive roller and the auxiliary roller.
The image forming apparatus according to claim 1 or 2, wherein the contact portion is provided only at both ends of the shaft portion. 3. The third aspect of the present invention includes an arm member that rotatably supports the shaft portion of the connecting roller, and an urging member that urges the arm member in a direction of pressing the connecting roller against the driving roller and the auxiliary roller. The image forming apparatus according to the description. The image forming apparatus according to any one of claims 1 to 4, further comprising a first disconnection mechanism for detaching the connecting roller from the driving roller and the auxiliary roller. The image forming apparatus according to claim 5, wherein the first detaching mechanism includes a second arm member that rotatably supports the connecting roller around the axis of the driving roller by moving the arm member. A second detaching mechanism for detaching the plurality of primary transfer members from the plurality of photoconductor drums is provided.
The first disengagement mechanism is connected to the second disengagement mechanism, and the disengagement of the plurality of primary transfer members to the plurality of photoconductor drums and the disengagement of the connection roller to the drive roller and the auxiliary roller. The image forming apparatus according to claim 5 or 6, wherein the image forming apparatus is interlocked with the above.

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